System, Method, and Apparatus for Detecting Air in a Fluid Line Using Active Rectification

ABSTRACT

A circuit for detecting air, a related system, and a related method are provided. The circuit for detecting air includes a receiver connection and an air-detection circuit. The receiver connection is configured to provide a receiver signal. The air-detection circuit is in operative communication with the receiver connection to process the receiver signal to generate a processed signal corresponding to detected air. The air-detection circuit includes one or more active-rectifying elements configured to actively rectify the receiver signal to provide the processed signal.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation application of U.S. patentapplication Ser. No. 14/101,848, entitled System, Method, and Apparatusfor Detecting Air in a Fluid Line Using Active Rectification, filed onDec. 10, 2013, now U.S. Publication No. US 2014-0165703-A1, published onJun. 19, 2014 (Attorney Docket No. L05), which claims priority to andthe benefit of U.S. Provisional Patent Application Ser. No. 61/738,447,filed Dec. 18, 2012 and entitled System, Method, and Apparatus forDetecting Air in a Fluid Line Using Active Rectification, (AttorneyDocket No. J32) which is hereby incorporated herein by reference in itsentirety.

BACKGROUND

Relevant Field

The present disclosure relates to detecting (e.g., for estimating,tracking, or categorizing) gas (e.g., air bubbles) in a fluid line. Moreparticularly, the present disclosure relates to a system, method, andapparatus for detecting air in a fluid line using active rectification.For example, the present disclosure relates to a system, method, and/oran apparatus for detecting air bubbles in a fluid line used in variousmedical applications, such as intravenous infusion therapy, dialysis,transfusion therapy, peritoneal infusion therapy, bolus delivery,enteral nutrition therapy, parenteral nutrition therapy, hemoperfusiontherapy, fluid resuscitation therapy, or insulin delivery, among others.

Description of Related Art

In many medical settings, one common mode of medical treatment involvesdelivering fluids into a patient. The need may arise to rapidly infusetherapeutic fluid into the patient, accurately infuse the fluid into thepatient, and/or slowly infuse the fluid into the patient. Occasionally,air bubbles may form within the fluid line coupled to the patient whichmay then deliver the bubbles to the patient's tissue with thetherapeutic fluid.

Too much air delivered to a patient may be detrimental for a patient.For example, too much total air delivered to a patient during atreatment or too much air delivered to a patient during a timeframe(e.g., the last 10 minutes) may have adverse effects on the patient.Furthermore, air bubbles within the fluid line may offset the amount oftherapeutic fluid delivered to the patient. Patient outcomes may beimproved to account for any displaced therapeutic fluid by increasingthe amount of fluid infused to ensure that the desired amount oftherapeutic fluid is delivered to the patient.

Delivery of fluid into the patient may be facilitated by use of agravity-fed line (or tube) inserted into the patient. Typically, a fluidreservoir (e.g., an IV bag) is hung on a pole and is connected to thefluid tube. The fluid tube is sometimes coupled to a drip chamber fortrapping air and estimating fluid flow. Below the fluid tube may be amanually actuated valve used to adjust the flow of fluid. For example,by counting the number of drops formed in the drip chamber within acertain amount of time, a caregiver can calculate the rate of fluid thatflows through the drip chamber and adjust the valve (if needed) toachieve a desired flow rate.

Certain treatments require that the fluid delivery system strictlyadhere to the flow rate set by the caregiver. Typically, suchapplications use an infusion pump, but such pumps may not be used in allsituations or environments. Air detection may be used by a gravity fedinfusion treatment or an infusion pump assisted infusion treatment,among other medical applications.

SUMMARY

In one embodiment of the present disclosure, a system for detecting air(e.g., a bubble) is provided. The system may be part of an infusion pumpor may be part of a dialysis apparatus. The system includes atransmitter, a receiver, and an air-detection circuit. The transmitteris configured to transduce a driver signal to ultrasonic vibrations. Thereceiver is configured to receive the ultrasonic vibrations andtransduce the ultrasonic vibrations to provide a receiver signal.

The air-detection circuit is in operative communication with thereceiver to process the receiver signal to generate a processed signalcorresponding to detected air. In an embodiment, the air-detectioncircuit may include a rectification circuit, such as one having one ormore active rectifiers. For example, the air-detection circuit mayinclude one or more active-rectifying elements each configured toactively rectify the receiver signal to provide the processed signal.The receiver signal and the processed signal may be digital signalsembodied in a digital circuit or may be analog signals.

The transmitter and receiver are configured to pass the ultrasonicvibrations through a tube such that the processed signal corresponds todetected air within the tube. The tube may be a medical tube, anintravenous fluid tube, and/or may carry blood.

The air-detection circuit may compare the processed signal to apredetermined threshold to determine if a bubble exists within the tube

In some embodiments, the system may include an amplifier. The amplifiermay amplify the receiver signal or the processed signal.

In yet another embodiment, the system includes a sample-and-hold circuitconfigured to sample the processed signal to hold the processed signalfor at least a predetermined amount of time.

In yet another embodiment, the transmitter and receiver are configuredto pass the ultrasonic vibrations through a tube such that the processedsignal corresponds to detected air within the tube. The air-detectioncircuit may be configured to calculate a total amount of air passingthrough the tube utilizing a flow rate of fluid through the tube and theprocessed signal.

In yet another embodiment, the system includes first and secondconductive paths, first and second switches, a first amplifier, and afirst filter. The first conductive path provides a first polarity of thereceiver signal from the receiver. The second conductive path provides asecond polarity of the receiver signal from the receiver. The firstswitch is electrically coupled to the first and second conductive paths.The first switch is configured to switch a first switch output tobetween the first and second polarities of the receiver signal. Thefirst switch is an active-rectifying element. The second switch iselectrically coupled to the first and second conductive paths. The firstswitch is configured to switch a first switch output to between thefirst and second polarities of the receiver signal. The first amplifierhas a positive input and a negative input. The positive input is coupledto the first switch output and the negative input is coupled to thesecond switch output. The first amplifier provides a first amplifieroutput in accordance with the positive and negative inputs. The firstfilter is electrically coupled to the first amplifier output of thefirst amplifier to provide a first filter output.

One or more of the receiver signal, the processed signal, the firstamplifier output, and a first filter output is a digital signal embodiedin a digital circuit and/or an analog signal.

The first filter may be an integrator. The integrator may be reset aftera predetermined period of integration time. In another embodiment, thefirst filter may be a low-pass filter.

The first and second switches may be electronically controlled. Thefirst and second switches may be configured to receive a switchingsignal. The switching signal and the first and second switches may beconfigured to switch a polarity of the electrical coupling between thefirst amplifier and the receiver in accordance with the switchingsignal.

In yet another embodiment of the present disclosure, the first andsecond switches are configured to receive a switching signal. The firstand second switches switch such that the first switch output is coupledto the first polarity of the receiver signal about when the secondswitch output is coupled to the second polarity. The first and secondswitches switch such that the first switch output is coupled to thesecond polarity of the receiver signal about when the second switchoutput is coupled to the first polarity. The first and second switchesswitch in response to the switching signal. The switching signal mayhave a frequency that is at least substantially the same as (or equalto) a frequency of the ultrasonic vibrations. The switching signal mayhave a frequency equal to a frequency of the driver signal. Theswitching signal has a phase angle relative to the driver signal, whichmay be zero degrees or 90 degrees.

In yet another embodiment, the system further includes third and fourthswitches, a second amplifier, and a second filter. The third switch iselectrically coupled to the first and second conductive paths. The thirdswitch is configured to switch a third switch output to between thefirst and second polarities of the receiver signal. The fourth switch iselectrically coupled to the first and second conductive paths. Thefourth switch is configured to switch a fourth switch output to betweenthe first and second polarities of the receiver signal. The secondamplifier has a positive input and a negative input. The positive inputof the second amplifier is coupled to the third switch output and thenegative input of the second amplifier is coupled to the fourth switchoutput. The second amplifier provides a second amplifier output inaccordance with the positive and negative inputs. The second filter iscoupled to the second amplifier to provide a second filter output. Thesecond filter may be another integrator or a low-pass filter. The secondfilter (e.g., another integrator) may be reset after a predeterminedperiod of integration time. The third and/or fourth switches may beelectronically controlled.

The first and second switches may be configured to receive a firstswitching signal. The first switching signal and the first and secondswitches are configured to switch a polarity of the electrical couplingbetween the first amplifier and the receiver in accordance with thefirst switching signal. The third and fourth switches may be configuredto receive a second switching signal. The second switching signal mayhave a phase angle of 90 degrees relative to the first switching signal.The second switching signal and the third and fourth switches areconfigured to switch a polarity of the electrical coupling between thesecond amplifier and the receiver in accordance with the secondswitching signal. The first switching signal and the second switchingsignal is a digital signal embodied in a digital circuit and/or is ananalog signal.

The processed signal may be a square root of: a squared first filteroutput summed with a squared second filter output. A processor maydetermine that air exists in a fluid tube when the processed signal isbelow a predetermined threshold. The processor may estimate a bubblevolume using the flow rate of fluid within the tube and a period of timethe processed signal is below the predetermined threshold. The processormay be one of a microprocessor, a microcontroller, a CPLD, and a FPGA,which may generate the first and second switching signals.

In yet another embodiment of the present disclosure, the first andsecond switches are configured to receive a first switching signal. Thefirst and second switches switch in response to the first switchingsignal. The first and second switches switch such that the first switchoutput is coupled to the first polarity of the receiver signal aboutwhen the second switch output is coupled to the second polarity. Thefirst and second switches switch such that the first switch output iscoupled to the second polarity of the receiver signal about when thesecond switch output is coupled to the first polarity. The third andfourth switches are configured to receive a second switching signal. Thethird and fourth switches switch in response to the second switchingsignal. The third and fourth switches switch such that the third switchoutput is coupled to the first polarity of the receiver signal aboutwhen the fourth switch output is coupled to the second polarity.Finally, the third and fourth switches switch such that the third switchoutput is coupled to the second polarity of the receiver signal aboutwhen the fourth switch output is coupled to the first polarity. Thefirst and second switching signals may each have a frequency at leastsubstantially the same as a frequency of the ultrasonic vibrations. Thefirst and second switching signals may each have a frequency at leastsubstantially the same as a frequency of the driver signal. The firstswitching signal may have a phase angle of about 90 degrees relative tothe second switching signal. The first switching signal may have a phaseangle of 90 degrees relative to the second switching signal.

The air-detection circuit may include one or more amplifiers and theprocessed signal is used to mitigate at least one offset error of theamplifier using the processed signal.

In some embodiments, a temporal window of the processed signal in whichthe receiver is not receiving the ultrasonic vibrations is used tomitigate at least one offset error of the amplifier.

In yet another embodiment, the system further wherein the driver signalis configured to be generated in predetermined bursts having apredetermined burst frequency.

In yet another embodiment of the present disclosure, the one or moreactive-rectifying elements may be one or more single-pole, double-throwswitches. The single-pole, double-throw switches may be solid-stateswitches.

In yet additional embodiments, the one or more active-rectifyingelements may be one or more single-pole, single-throw switches, whichmay be solid-state switches.

In yet an additional embodiment of the present disclosure, the systemincludes first and second single pole, single throw switches. The firstsingle pole, single throw switch may be one of the active-rectifyingelements and is configured to provide electrical communication betweenthe receiver signal and a first switch output in accordance with a firstswitching signal. The second single pole, single throw switch may beconfigured to provide electrical communication between receiver signaland a second switch output in accordance with an inverted signal of theswitching signal. One or both of the first switching signal and theinverted signal of the switching signal may be digital signals embodiedin a digital circuit and/or analog signals.

The system may further includes a first amplifier configured to amplifythe receiver signal prior to electrical coupling with the first singlepole, single throw switch. The system further may also include a secondamplifier configured to amplify the receiver signal prior to electricalcoupling with the second single pole, single throw switch.

In yet another embodiment, the system includes third and fourth singlepole, single throw switches. The third single pole, single throw switchis configured to provide electrical communication between an inversionof the receiver signal and a third switch output in accordance with asecond switching signal. The fourth single pole, single throw switch isconfigured to provide electrical communication between the inversion ofthe receiver signal and a fourth switch output in accordance with aninverted signal of the switching signal. The first and second switchingsignals have a quadrature phase relationship.

An amplifier may be used and is configured to amplify the inversion ofthe receiver signal prior to electrical communication with one of thethird and fourth single, pole, single throw switches.

The system may further include a first integrator such that the firstswitch output and a second switch output are in electrical communicationwith the first integrator to integrate a signal therefrom to provide afirst integrator output. The first integrator may be reset after a firstpredetermined period of time. The system may include a firstsample-and-hold circuit configured to operatively sample and hold thefirst integrator output.

The system may yet also include a second integrator such that the thirdswitch output and the fourth switch output are in electricalcommunication with the second integrator to integrate a signal therefromto provide a second integrator output. The second integrator may bereset after a second predetermined period of time. The system mayinclude a second sample-and-hold circuit configured to operativelysample and hold the second integrator output.

The first and second switching signals may be synchronized to the driversignal.

The processed signal is a square root of: a squared first integratoroutput summed with a squared second integrator output. The system mayfurther include a processor configured to determine whether air existswhen the processed signal is below a predetermined threshold.

The first and second integrators may integrate for a predeterminednumber of cycles of the driver cycles a predetermined period of timeafter the driver signal is driving the transmitter.

The first integrator can integrate for a predetermined number of cyclesof the driver signal for a predetermined period of time after the driversignal drives the transmitter such that the ultrasonic vibrations havepassed the receiver. The first integrator output is used to adjust anoffset of the first integrator.

The second integrator may integrate for a predetermined period tocapture all of the ultrasonic vibrations passing the receiver. Thesecond integrator output may be used to adjust an offset of the firstsecond.

The system may further include a first sample-and-hold circuit to hold avoltage of the first integrator output for the processor to determinethe processed signal, a first diagnostic sample-and-hole circuit to holdthe voltage of the first integrator output to adjust an offset of thefirst integrator, a second sample-and-hold circuit to hold a voltage ofthe second integrator output for the processor to determine theprocessed signal, and a second diagnostic sample-and-hole circuit tohold the voltage of the second integrator output to adjust an offset ofthe second integrator.

The first and second switching signals may be generated using at leastone of a processor, a FPGA, a CPLD, and an oscillator. The processedsignal may a vector defined by the first integrator output and thesecond integrator output and a processor may perform an integrity checkby determining if a phase angle of the processed signal is within apredetermined range.

In one embodiment of the present disclosure, a method of detecting airis provided. The method for detecting air may include transmittingultrasonic energy, receiving the ultrasonic energy, transducing thereceived ultrasonic energy into a receiver signal, and activelyrectifying the receiver signal to provide a processed signal. The methodmay also include determining whether the processed signal is less that apredetermined threshold.

The method may include the transmitting act is performed by anultrasonic transducer. The ultrasonic transducer may be a piezoelectricceramic. In another embodiment the transducing act may be performed byan ultrasonic transducer. The ultrasonic transducer may be apiezoelectric ceramic.

In yet some additional embodiments, the act of actively rectifying thereceiver signal to provide the processed signal may be synchronouslyrectifying the receiver signal to provide the processed signal. In someembodiments, the act of transmitting the ultrasonic energy may includetransmitting the ultrasonic energy through a tube.

In yet another embodiment of the method, the act of actively rectifyingthe receiver signal to provide the processed signal includes: invertingthe receiver signal to provide an inverted receiver signal, switchingbetween the receiver signal and the inverted receiver signal inaccordance with a first switching signal to provide a first switchoutput, integrating the first switch output to provide a firstintegrated output, switching between the receiver signal and theinverted receiver signal in accordance with a second switching signal toprovide a second switch output, integrating the second switch output toprovide a second integrated output, and calculating a magnitude usingthe first and second integrated outputs, wherein the magnitude definesthe processed signal.

The method may further include determining that air exists within a tubeif the magnitude is less that the predetermined threshold.

In yet some additional embodiments of the method, the first and secondswitching signals may each have a frequency equal to a dominantfrequency of the ultrasonic energy. The first and second switchingsignal may be ninety degrees out of phase relative to each other. Thefirst and second switching signal may be about ninety degrees out ofphase relative to each other.

In some embodiments, at least one of the receiver signal, the invertedreceiver signal, the first switch output, the second switch output, thefirst integrate output, and the second integrated output may beamplified by an amplifier.

In yet other embodiments, the act of switching between the receiversignal and inverted receiver signal in accordance with a first switchingsignal to provide a first switch output may be configured using at leastone of a semiconductor switch, a MOSFET, a single pole, single throwswitch, a single pole double throw switch, a single pole changeoverswitch, a double pole double throw switch, a four-way switch, atransistor, a BJT transistor, and a relay switch.

In some embodiments, the method may be at least partially implemented bya circuit on an infusion pump configured to detect air in an intravenoustube.

In some embodiments, the act of actively rectifying the receiver signalto provide the processed signal may include: activating a firstswitching network configured to switch between the receiver signal andan inverted receiver signal to provide a first switching network signal,switching between the receiver signal and the inverted receiver signalin accordance with a first switching signal to provide the firstswitching network signal, integrating the first switching network signalto provide a first integrated output, activating a second switchingnetwork configured to switch between the receiver signal and an invertedreceiver signal to provide a second switching network signal, switchingbetween the receiver signal and the inverted receiver signal inaccordance with a second switching signal to provide the secondswitching network signal, wherein the second switching signal is about90 degrees out of phase with the first switching signal, integrating thesecond switching network signal to provide a second integrated output,and generating a processed signal using the first and second integratedoutputs.

In some embodiments, the first switching network may comprise two singlepole, double throw switches. The second switching network may comprisetwo single pole, double throw switches. The processed signal may be amagnitude calculated by using the first and second integrated outputs.

In some embodiments, the act of actively rectifying the receiver signalto provide a processed signal may comprise: amplifying the receiversignal with a positive gain using a first amplifier, amplifying thereceiver signal with a negative gain using a second amplifier, switchingbetween outputs of the first and second amplifiers in accordance with afirst switching signal to generate a first switch output, filtering thefirst switch output to provide a first filtered output, switchingbetween the outputs of the first and second amplifiers to generate asecond switch output. The second switching signal may be one of equal toor about equal to ninety degrees out of phase with the first switchingsignal. The second switching output may be filtered to provide a secondfiltered output. A processed signal may be generated using the first andsecond filtered outputs.

In another embodiment of this method, the processed signal is amagnitude. The method may further include the acts of: resetting thefirst filtered output (e.g., resetting the first integrated output); andresetting the second filtered output (e.g., resetting the secondintegrated output).

In some embodiments, the act of filtering the first switch output toprovide the first filtered output is the act of integrating the firstswitch output to provide a first integrated output, wherein the firstfiltered output is the first integrated output. Additionally oralternatively, the act of filtering the second switch output to providethe second filtered output may be the act of integrating the secondswitch output to provide a second integrated output, wherein the secondfiltered output is the second integrated output.

The act of generating the processed signal using the first and secondfiltered outputs may be the act of generating the processed signal usingthe first and second integrated outputs. The act of determining whetherthe processed signal is less that a predetermined threshold may be theact of determining that air exists within the tube if the magnitude isless that a predetermined threshold.

In some additional embodiments, the method may include: sampling theprocessed signal and holding the processed signal; determining whetherair exists within a tube using the processed signal; determining a totalvolume of air passing within the tube using the processed signal and aflow rate of fluid within the tube; and/or adjusting at least one offsetgain using the processed signal during a period where there is anabsence of the ultrasonic energy. The act of sampling the processedsignal and holding the processed signal may be performed by asample-and-hold circuit.

In yet another embodiment of the present disclosure, a system fordetecting air includes a transmitter means, a receiver means, and anair-detection means. The transmitter means is a means for transducing adriver signal to ultrasonic vibrations. The receiver means is a meansfor receiving the ultrasonic vibrations and transducing the ultrasonicvibrations to provide a receiver signal. The air-detection means is ameans for actively rectifying the receiver signal to provide a processedsignal

In yet another embodiment of the present disclosure, a method fordetecting air includes the acts of: a transmitting step for transmittingultrasonic energy; a receiving step for receiving the ultrasonic energy;a transducing step for transducing the received ultrasonic energy into areceiver signal; a rectifying step for actively rectifying the receiversignal to provide a processed signal; and a determining step fordetermining whether the processed signal is less that a predeterminedthreshold.

In yet another embodiment of the present disclosure, a circuit includesa receiver connection and an air-detection circuit. The receiverconnection is configured to provide a receiver signal. The air-detectioncircuit is in operative communication with the receiver connection toprocess the receiver signal to generate a processed signal correspondingto detected air. The air-detection circuit comprising one or moreactive-rectifying elements configured to actively rectify the receiversignal to provide the processed signal. The air-detection circuit maycompare the processed signal to a predetermined threshold to determineif a bubble exists within a tube.

In yet another embodiment of the present disclosure, the circuit alsoincludes first and second conductive paths, first and second switches, afirst amplifier, and a first filter. The first conductive path providesa first polarity of the receiver signal from the receiver connection.The second conductive path provides a second polarity of the receiversignal from the receiver connection. The first switch is electricallycoupled to the first and second conductive paths. The first switch isconfigured to switch a first switch output to between the first andsecond polarities of the receiver signal. The first switch defines theat least one active-rectifying element. The second switch iselectrically coupled to the first and second conductive paths. The firstswitch configured to switch a first switch output to between the firstand second polarities of the receiver signal. The first amplifier havinga positive input and a negative input. The positive input is coupled tothe first switch output and the negative input is coupled to the secondswitch output, wherein the first amplifier provides a first amplifieroutput in accordance with the positive and negative inputs. The firstfilter electrically coupled to the first amplifier output of the firstamplifier to provide a first filter output. The first filter may be anintegrator.

The first and/or second switches may be configured to receive aswitching signal. The first and/or second switches may switch such thatthe first switch output is coupled to the first polarity of the receiversignal about when the second switch output is coupled to the secondpolarity. The first and/or second switches may switch such that firstswitch output is coupled to the second polarity of the receiver signalabout when the second switch output is coupled to the first polarity.The first and/or second switches may switch in response to the switchingsignal.

A third switch may be electrically coupled to the first and secondconductive paths. A third switch may be configured to switch a thirdswitch output to between the first and second polarities of the receiversignal. A fourth switch electrically coupled to the first and secondconductive paths. A fourth switch may be configured to switch a fourthswitch output to between the first and second polarities of the receiversignal. The third and/or fourth switches may be electronicallycontrolled. A second amplifier may have a positive input and a negativeinput such that the positive input of the second amplifier is coupled tothe third switch output and the negative input of the second amplifieris coupled to the fourth switch output. The second amplifier provides asecond amplifier output in accordance with the positive and negativeinputs. The second filter coupled to the second amplifier to provide asecond filter output. The second filter may be another integrator. Theanother integrator is reset after a predetermined period of integrationtime. The second filter may be a low-pass filter.

The first and second switches may be configured to receive a firstswitching signal. The first switching signal and/or the first and secondswitches may be configured to switch a polarity of the electricalcoupling between the first amplifier and the receiver connection inaccordance with the first switching signal. The third and fourthswitches may be configured to receive a second switching signal. Thesecond switching signal may have a phase angle of 90 degrees relative tothe first switching signal. The second switching signal and/or the thirdand fourth switches may be configured to switch a polarity of theelectrical coupling between the second amplifier and the receiverconnection in accordance with the second switching signal.

The first and/or second switches may be configured to receive a firstswitching signal. The first and/or second switches may switch inresponse to the first switching signal. The first and/or second switchesmay switch such that the first switch output is coupled to the firstpolarity of the receiver signal about when the second switch output iscoupled to the second polarity. The first and/or second switches mayswitch such that the first switch output is coupled to the secondpolarity of the receiver signal about when the second switch output iscoupled to the first polarity. The third and/or fourth switches may beconfigured to receive a second switching signal. The third and/or fourthswitches may switch in response to the second switching signal. Thethird and/or fourth switches may switch such that the third switchoutput is coupled to the first polarity of the receiver signal aboutwhen the fourth switch output is coupled to the second polarity. Thethird and/or fourth switches may switch such that the third switchoutput is coupled to the second polarity of the receiver signal aboutwhen the fourth switch output is coupled to the first polarity.

In yet some additional embodiments, the circuit includes first andsecond single pole, single throw switches. The first single pole, singlethrow switch defines the one or more active-rectifying elementsconfigured to provide electrical communication between the receiversignal and a first switch output in accordance with a first switchingsignal. The second single pole, single throw switch may be configured toprovide electrical communication between receiver signal and a secondswitch output in accordance with an inverted signal of the switchingsignal.

A third single pole, single throw switch may be configured to provideelectrical communication between an inversion of the receiver signal anda third switch output in accordance with a second switching signal. Afourth single pole, single throw switch may be configured to provideelectrical communication between the inversion of the receiver signaland a fourth switch output in accordance with an inverted signal of theswitching signal.

A first integrator may be used by the circuit. The first switch outputand a second switch output may be in electrical communication with thefirst integrator to integrate a signal therefrom to provide a firstintegrator output. Also, a second integrator may be used by the circuitsuch that the third switch output and the fourth switch output are inelectrical communication with the second integrator to integrate asignal therefrom to provide a second integrator output.

The first integrator may integrate for a predetermined number of cyclesof the driver cycles for a predetermined period of time after the driversignal is driving a transmitter such that the ultrasonic vibrations havepassed a receiver coupled to the receiver connector. The firstintegrator output may be used to adjust an offset of the firstintegrator. The second integrator may integrate for the predeterminedperiod to capture all of the ultrasonic vibrations passing a receivercoupled to the receiver connection. The second integrator output is usedto adjust an offset of the first second.

This embodiment may also include first and second sample-and-holdcircuits, and first and second diagnostic sample-and-hole circuits. Thefirst sample-and-hold circuit may hold a voltage of the first integratoroutput for the processor to determine the processed signal. The firstdiagnostic sample-and-hole circuit may hold the voltage of the firstintegrator output to adjust an offset of the first integrator. Thesecond sample-and-hold circuit may hold a voltage of the secondintegrator output for the processor to determine the processed signal.The second diagnostic sample-and-hole circuit may hold the voltage ofthe second integrator output to adjust an offset of the secondintegrator.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a block diagram of a system for infusing fluid into apatient having an air detector system that detects air a fluid lineusing active rectification in accordance with an embodiment of thepresent disclosure;

FIG. 2 shows a block diagram of a system for detecting air in a fluidline using active rectification in accordance with an embodiment of thepresent disclosure;

FIG. 3 shows a flow chart diagram of a method for detecting air in afluid line using active rectification in accordance with an embodimentof the present disclosure;

FIG. 4 shows a schematic diagram of a circuit for detecting air in afluid line using active rectification in accordance with an embodimentof the present disclosure;

FIG. 5 shows a flow chart diagram of a method for detecting air in afluid line, e.g., using the circuit of FIG. 4, in accordance with anembodiment of the present disclosure;

FIG. 6 shows a schematic diagram of a circuit for detecting air in afluid line using active rectification in accordance with an embodimentof the present disclosure;

FIG. 7 shows a flow chart diagram of a method for detecting air in afluid line, e.g., using the circuit of FIG. 6, in accordance with anembodiment of the present disclosure

FIGS. 8A-8B show a circuit schematic for detecting air in a fluid lineusing active rectification in accordance with an embodiment of thepresent disclosure;

FIGS. 9-12 show several signal vs. time traces to illustrate theoperation of the circuit shown as the circuit schematic of FIGS. 8A-8Bin accordance with an embodiment of the present disclosure;

FIGS. 13A-15 illustrate a schematic of a circuit for detecting air in afluid line using active rectification in accordance with an embodimentof the present disclosure;

FIGS. 16-19 show several signal vs. time traces to illustrate theoperation of the circuit shown in the circuit schematic of FIGS. 13A-15in accordance with an embodiment of the present disclosure;

FIG. 20 shows a schematic for providing a compensating reference voltagein accordance with an embodiment of the present disclosure;

FIGS. 21A and 21B show the operation of the compensating referencevoltage in accordance with an embodiment of the present disclosure;

FIGS. 22A-23B show a circuit for detecting the presence of air within atube in accordance with another embodiment of the present disclosure;and

FIGS. 24A-26C show a circuit for detecting the presence of air withintwo tubes in accordance with another embodiment of the presentdisclosure.

DETAILED DESCRIPTION

FIG. 1 shows a block diagram of a system 1 for infusing fluid into apatient 5 having an air detector system 4 that detects air in a fluidline 6 using active rectification in accordance with an embodiment ofthe present disclosure. The system 1 may be used to treat a patient 5,such as a human or animal (e.g., pets). The system 1 may be part of anintravenous infusion therapy, a dialysis therapy, a transfusion therapy,a peritoneal infusion therapy, a bolus delivery, an enteral nutritiontherapy, a parenteral nutrition therapy, a hemoperfusion therapy, afluid resuscitation therapy, or insulin delivery, among others.

The system 1 includes a fluid container 2 that contains fluid coupled toa fluid line 6. The fluid may flow from the fluid container 2, throughthe fluid line 6, through a pump 3 and into a patient 5 through a distalportion of the fluid line 6.

The pump 3 includes an air detector system 4 for detecting (e.g.,estimating, tracking, or categorizing) air that flows through the pump3. The pump 3 may be a peristaltic pump, such as a finger-typeperistaltic pump. The pump 3 may modify, adjust, or account for airdelivered to the patient as determined by the air detector system 4.

The air detector system 4 may use active rectification (describedbelow), such as synchronous rectification. The pump 3 may issue an alarmor alert when: (1) the total amount of air that passes the air detectorsystem 4 during a therapy session exceeds a first predeterminedthreshold; (2) the amount of air that passes the air detector system 4during a predetermined period of time exceeds a second predeterminedthreshold; and/or (3) the amount of air that passes the air detectorsystem 4 during the latest predetermined amount of time exceeds a thirdpredetermined threshold. The first, second, and/or third predeterminedthresholds may be the same or may be different from each other. The airdetector system 4 may keep track of the air by volume or by weight,and/or may account for the temperature of the air and/or the fluidwithin the fluid line 6 when detecting the air flowing therethrough.

FIG. 2 shows a block diagram of a system 18 for detecting air (e.g., abubble 7) in the fluid line 6 using active rectification in accordancewith an embodiment of the present disclosure. The system 18 of FIG. 2may be the air detector system 4 of FIG. 1. The system 18 includes adriver circuit 10, a transmitter 11, a receiver 8, an air detectioncircuit 9, a clock 12 and a processor 17. The system 18 detects air,such as the air bubble 7, in the fluid line 6. The system 18 uses activerectification, and in some embodiments it uses synchronousrectification, in the air detection circuit 9 to detect air 7 within thefluid line 6, as described below.

The processor 17 signals the driver circuit 10 (via path 15) to drivethe transmitter 11 with a drive signal. The transmitter 11 receives thedrive signal from the driver circuit 10 to generate ultrasonic energywhich is transmitted through the tube 6 to the receiver 8. The receiver8 receives the ultrasonic energy and transduces the ultrasonic energyinto an electric signal. The air detection circuit 9 receives theelectric signal for processing therein to provide a processed signal.The processed signal corresponds to air and/or the absence of air withinthe fluid tube 6.

The air detection circuit 9 provides the processed signal to theprocessor 17 via path 16. The processor 17 uses the processed signal todetect air within the tube 6. For example, the processor 17 may issue analarm or an alert when (1) the total amount of air that passes betweenthe transmitter 11 and receiver 8 during a therapy session exceeds afirst predetermined threshold; (2) the amount of air that passes betweenthe transmitter 11 and receiver 8 during a predetermined period of timeexceeds a second predetermined threshold; and/or (3) the amount of airthat passes between the transmitter 11 and receiver 8 during the latestpredetermined amount of time exceeds a third predetermined threshold.

The air detection circuit 9 uses active rectification to rectify theelectric signal from the receiver 8 to provide the processed signal tothe processor 17 via a path 16. In some embodiments of the presentdisclosure, the air detection circuit 9 and the driver circuit 10receive a clock signal from a common clock 12 from a path 14 and a path13, respectively, such that the air detection circuit 9 synchronizes theactive rectification with the ultrasonic energy from the transmitter orwith the clock 12 to thereby perform synchronous rectification.

The clock 12 generates a reference signal that is sent to the airdetection circuit 9 via a path 14 and to the driver circuit 10 via apath 13. The clock 12 may be a semiconductor device, a crystal-baseddevice, a 555-timer configured to generate a cyclical signal, a waveformgenerator, or any circuit, semiconductor or device that can provide atime reference. The signals sent from the clock 12 may be in the form ofa square wave, a pulse-width-modulation signal, a periodic wave, adigital signal, or any other way of communicating information about atime reference. In some embodiments of the present disclosure, the clock12 is part of or is generated by the processor 17. In yet additionalembodiments of the present disclosure, the clock 12 is used as thesystem clock by the processor 17. Additionally or alternatively, theprocessor 17 may receive a clock signal from the clock 12 to coordinateits operation with other components that utilizes the clock 12.

The driver circuit 10 is configured to drive the transmitter 11 andreceives a clock signal via the path 13. The driver circuit 10 mayinclude appropriate buffers, amplifiers, and power-related circuitry todrive the transmitter 11. The driver circuit 10 may be a singlesemiconductor device, may be multiple semiconductor devices, may use nosemiconductor devices, may comprise one or more passive components,and/or may be a prepackaged driver circuit. The driver circuit 10 mayreceive electrical power from a power supply (not shown in FIG. 2) toprovide sufficient power to drive the transmitter 11. The driver circuit10 may receive an enable signal via a path 15 from the processor 17. Theenable signal from the processor 17 may be in the form of a square wave,a pulse-width-modulation signal, a pulse signal, a digital signal, orany other way of communicating information to the driver circuit. In onespecific embodiment of the present disclosure, the driver circuit 10amplifies the clock signal from the clock 12. The driver circuit 10 maydrive the transmitter 11 for a predetermined number of cycles (e.g., 6cycles).

The transmitter 11 tranduces an electric signal received from the drivercircuit 10 to ultrasonic energy. The transmitter 11 may be an ultrasonictransducer, a magnetostrictive transducer, a piezoelectric transducer, apiezoelectric crystal, a piezoelectric ceramic, a capacitive actuationtransducer, or other transducer technology.

The transmitter 11 transmits ultrasonic energy through the tube 6. Thetube 6 may be a medical tube, such as, for example, an intravenous tubeused for intravenous therapy or a tube used in dialysis. The tube 6 maybe flexible or rigid and may be held in place by a holder (not shown).

The receiver 8 receives the ultrasonic energy that has, preferably, beenpropagated through the tube 6. The receiver 8 transduces the ultrasonicenergy into a receiver signal that is an electrical signal and providesit for processing by the air detection circuit 9. The receiver 8 may bemade of the same material as the transmitter 11 or may utilize the sametechnology as previously described.

The air detection circuit 9 uses the signal from the receiver 8 toactively rectify the signal therefrom to provide a processed signal. Theprocessed signal may correspond to the magnitude of the ultrasonicenergy received by the receiver 8 and/or the magnitude of the receiversignal from the receiver 8. The air detection circuit 9, in somespecific embodiments, may use active rectification and thereby may besynchronized with the signal from the clock 12. The air detectioncircuit 9 may comprise one or more of: (1) a semiconductor device, (2)an analog device, (3) an amplifier, (4) a quadrature signal, (5) aprocessing device, such as a processor, a microprocessor, amicrocontroller, a FPGA, a CPLD, a PAL, a PLD, etc., or (6) any othercircuitry. In some embodiments, the processor 17 is part of the airdetection circuit 9.

The processor 17 uses the processed signal from the air detectioncircuit 9 to determine if/when air exists within the tube 6, e.g., thebubble 7. The processor 17 may, for example, determine that air does notexist within the tube 6 between the transmitter 11 and the receiver 8 ifthe processed signal is above a predetermined threshold. Likewise, theprocessor 17 may determine that air does exist within the tube 6 if theprocessed signal is below a predetermined threshold.

The various paths 13, 14, 15, and 16 that couple various componentstogether within the system 18 may be conductive paths (e.g., metallayers in a PCB board), may be analog lines, may be digital lines, maybe optical lines, may be electromagnetic lines, or may be another othersufficient communications paths.

FIG. 3 shows a flow chart diagram of a method 19 for detecting air in afluid line using active rectification in accordance with an embodimentof the present disclosure. The method 19 may be implemented using thesystem 18 of FIG. 2. The method 19 includes acts 20-24, in which act 23includes acts 25-30 and act 24 includes act 31.

Act 20 transmits ultrasonic energy through a tube. Act 20 may beperformed by using, for example, the transmitter 11 of FIG. 2. Act 21receives the ultrasonic energy passed through the tube. Act 22transduces the received ultrasonic energy into a receiver signal, e.g.,using the receiver 8 of FIG. 2. Act 23 actively rectifies the receiversignal to provide a processed signal. Act 23 may be performed by an airdetection circuit, such as the air detection circuit 9 of FIG. 2.

In one specific embodiment of the present disclosure, act 23 includesact 25 through act 30. Acts 25-30 may be performed by an air detectioncircuit, e.g., the air detection circuit 9 of FIG. 1. Act 25 inverts thereceiver signal to provide an inverted receiver signal. Act 26 switchesbetween the receiver signal and the inverted receiver signal inaccordance with a first switching signal to provide a first switchoutput. In some specific embodiments, act 26 may be performed by usingone or more switches. Act 27 integrates the first switch output toprovide a first integrated output. Act 27 may integrate the first switchoutput for a predetermined number of cycles (e.g., a predeterminednumber of cycles of the ultrasonic energy or of the clock, such as theclock 12 of FIG. 2). Act 27 may further include resetting any integratorcircuit or algorithm prior to integrating, if appropriate. Act 28switches between the receiver signal and the inverted receiver signal inaccordance with a second switching signal to provide a second switchoutput. The second switching signal is about 90 degrees out of phasewith the first switching signal. Act 28 may be performed by using one ormore switches. Act 29 integrates the second switch output to provide asecond integrated output. Act 30 generates a processed signal (e.g., amagnitude) using the first and second integrated outputs.

Act 24 determines whether the processed signal is less that apredetermined threshold. Act 24 may include act 31. Act 31 determinesthat air exists within the tube if the magnitude is less that apredetermined threshold. The magnitude of act 31 is the magnitude of theprocessed signal.

FIG. 4 shows a schematic diagram of a circuit 32 for detecting air in afluid line using active rectification in accordance with an embodimentof the present disclosure. The circuit 32 of FIG. 4 may be the airdetection circuit 9 of FIG. 2, in some specific embodiments.

The circuit 32 is coupled to a receiver, such as the receiver 8 of FIG.2, via positive sense 42 and negative sense 43. The positive sense 42 iscoupled to one of the terminals of a receiver, and the negative sense 43is coupled to another terminal of the receiver. In some embodiments ofthe present disclosure, one of the positive or negative senses 42 or 43is coupled to a common reference; for example, the negative sense 43 maybe coupled to a ground of the circuit 32.

The positive sense 42 is electrically coupled to a first switch 35 viaits terminal 1 and to a second switch 36 via its terminal 2. Thenegative sense 43 is electrically coupled to the first switch 35 via itsterminal 2 and to the second switch 36 via its terminal 1. The switches35, 36 are single-pull, double throw switches. The switches 35, 36receive a clock signal 45 (operating as a switching signal) viarespective terminals 4. That is, in the arrangement shown in FIG. 4, theswitches 35, 36 are electronically controlled by the clock 45. Forexample, for both of the switches 35, 36, a high value from the clock 45may cause the switch output at terminal 3 to be electrically coupled tothe terminal 1 and a low value from the clock 45 may cause the switchoutput at terminal three to be electrically coupled to terminal 2. Insome embodiments, the terminal selection caused by the clock signal 45may be reversed. In yet additional embodiments, the transition of theclock 45 can cause the switches 35, 36 to change states (i.e., whichinput terminal is electrically coupled to the output terminal).

The switch output (terminal 3) of the first switch 35 is electricallycoupled to the positive terminal of the first amplifier 33 and theswitch output (terminal 3) of the second switch 36 is coupled to thenegative terminal of the first amplifier.

The arrangement shown for the first and second switches 35, 36, and theamplifier 33 are such that the polarity of the signal received from thereceiver changes depending on the whether the clock 45 is high or low.That is, the clock 45 causes the first amplifier 33 to either amplifythe signal from the receiver or its inverted signal in accordance withthe clock 45.

In some embodiments of the present disclosure, the amplifier 33 may havea gain of 1, may be a buffer, may have a gain of less than 1, or mayhave a gain of more than 1. The output of the first amplifier 33 is fedinto a first filter 39.

The first filter 39 may be a first integrator that integrates the signalfrom the amplifier 33 to provide a first integrated output (i.e., afirst integrated signal). For example, the first filter 39 may integratethe output from the first amplifier 33 for a predetermined amount oftime corresponding to an expected time in which the receiver receivesultrasonic energy; the integrator may be reset for each pulse ofultrasonic energy. In some embodiments, the predetermined amount of timemay include periods of time before and after the ultrasonic energy isexpected to be received by the receiver to ensure all of the ultrasonicenergy is used to generate the first integrated output. The ultrasonicenergy may be generated in a pulse of energy having a plurality ofperiodic waveforms, such as, for example, 6 cycles of a sine wave. Thefirst filter 39 provides the first integrated output (labeled as Out X)that is fed into the magnitude detection component 41.

Also coupled to the positive sense 42 and the negative sense 43 are athird switch 37 and a fourth switch 38. The outputs of the third andfourth switches 37, 38 are fed into a second amplifier 34. The third andfourth switches 37, 38 and the second amplifier 34 are arranged suchthat the polarity of the signal from the receiver (received as thepositive sense 42 and the negative sense 43) is switched in accordancewith a quadrature clock 46. That is, the clock 46 has the same frequencyas the clock 45 but is out of phase by 90 degrees relative to the clock45.

The clock 45 and the quadrature clock 46 may be generated from the clock12 of FIG. 2, or may be generated by the clock 12 and sent via a path 14to the circuit 32. In yet additional embodiments of the presentdisclosure, the clock 45 may be generated by the clock 12 of FIG. 2which is used to generate the quadrature clock 46, e.g., using aphase-locked loop. In yet additional embodiments, a logic device, suchas a CPLD or a FPGA, is used to generate the clock 45 and quadratureclock 46 which may also generate a clock used in generating the driversignal to the transmitter 11 (see FIG. 2).

The output of the second amplifier 34 is fed into a second filter 40,which may be a second integrator. The second filter 40 provides a secondintegrated output (labeled as output Y) which is fed into the magnitudedetection component 41.

The magnitude detection component 41 calculates the magnitude of thesignal received by the receiver via the positive sense 42 and thenegative sense 43. The out X signal may define an x-component of avector and the out Y signal may define a y-component of the same vector.Therefore, the magnitude 44 is calculated using by taking the squareroot of the squared output from the first filter 39 summed with thesquared output from the second filter 40. That is, the magnitude 44 iscalculated using Formula (1) as follows:

Magnitude=√{square root over (Outx ²+Outy ²)}  (1).

In other embodiments of the present disclosure, a reference value may beused to ensure that any signal swings are within a predetermined range.For example, one or more op-amps that are used within a circuit mayoutput a signal between ground and the power supply. A reference voltagemay be used to offset the output of the op-amps such that the outputsignal does not reach a limit of the op-amp's voltage range (e.g., arail of the op-amp). In this embodiment, Formula (1) above is modifiedto include the reference voltage as illustrated in Formula (2) asfollows:

$\begin{matrix}{{Magnitude} = {\sqrt{( {{Outx} - {{reference}\mspace{14mu} {Voltage}_{1}}} )^{2} + ( {{Outy} - {{reference}\mspace{14mu} {Voltage}_{2}}} )^{2}}.}} & (2)\end{matrix}$

In some embodiments, the referenceVoltage₁ may be equal to thereferenceVoltage₂.

In some embodiments of the present disclosure, outputs of any op-ampsused may produce an offset error, which may be accounted for. In someembodiments of the present disclosure, these errors are accounted for inaccordance with Formula (3) as follows:

$\begin{matrix}{{Magnitude} = {\sqrt{\begin{matrix}{( {{Outx} - {{reference}\mspace{14mu} {Voltage}_{1}} - {{offset}\mspace{14mu} {Voltage}_{1}}} )^{2} +} \\( {{Outy} - {{reference}\mspace{14mu} {Voltage}_{2}} - {{offset}\mspace{20mu} {Voltage}_{2}}} )^{2}\end{matrix}}.}} & (3)\end{matrix}$

In some embodiments, the referenceVoltage₁ may be equal to thereferenceVoltage₂. In yet some additional embodiments, theoffsetVoltage₁ may be equal to the offsetVoltage₂. In some embodimentsof the present disclosure, the reference voltage is modified to accountfor any error offsets such that the reference voltage is a compensatingreference voltage. That is, the compensating reference voltagecompensates for offset errors. Therefore, Equation (2) may be usedbecause the reference voltages are modified prior to being used in thecircuit.

The magnitude 44 corresponds to the magnitude of the ultrasonic energyreceived by the receiver that is coupled to the circuit 32 via thepositive sense 42 and the negative sense 43.

FIG. 5 shows a flow chart diagram of a method 47 for detecting air in afluid line, e.g., using the circuit of FIG. 4, in accordance with anembodiment of the present disclosure.

The method 47 includes acts 48, 49, 50, 51 and 60. Act 51 may includeacts 53-59 as subparts. Act 60 may include act 61 as a subpart.

Act 48 transmits ultrasonic energy through a tube. Act 49 receives theultrasonic energy passed through the tube. Act 50 transduces thereceived ultrasonic energy into a receiver signal. Act 51 activelyrectifies the receiver signal to provide a processed signal. Act 60determines whether the processed signal is less that a predeterminedthreshold.

Act 51 may include acts 53 through act 59. Act 53 activates a firstswitching network (e.g., the two single pole, double throw switches 35and 36 of FIG. 4) configured to switch between the receiver signal andan inverted receiver signal to provide a first switching network signal.For example, act 51 may activate the first switching network byproviding power thereto and/or starting a first switching signal.

Act 54 switches between the receiver signal and the inverted receiversignal in accordance with a first switching signal to provide the firstswitching network signal. Optionally, an amplifier, e.g., the amplifier33 of FIG. 4, is part of the switching network and amplifies the firstswitching network signal. Act 55 integrates the first switching networksignal to provide a first integrated output. Act 56 activates a secondswitching network (e.g., the two single pole, double throw switches)configured to switch between the receiver signal and an invertedreceiver signal to provide a second switching network signal. Act 57switches between the receiver signal and the inverted receiver signal inaccordance with a second switching signal to provide the secondswitching network signal. The second switching signal is about 90degrees out of phase with the first switching signal. Optionally, anamplifier, e.g., the amplifier 34 of FIG. 4, is part of the switchingnetwork and amplifies the second switching network signal. Act 58integrates the second switching network signal to provide a secondintegrated output. Act 59 generates a processed signal (e.g., amagnitude) using the first and second integrated outputs.

Act 60 may include act 61, which determines that air exists within thetube if the magnitude is less that a predetermined threshold.

FIG. 6 shows a schematic diagram of a circuit 62 for detecting air in afluid line using active rectification in accordance with an embodimentof the present disclosure. The circuit 62 includes a first amplifier 63,a second amplifier 64, a first filter 68, a second filter 69, and amagnitude detection component 70.

A source 65 represents the signal from an ultrasonic transducer thatreceives ultrasonic energy, e.g., a receiver signal electrically coupledto the ultrasonic transducer. The source 65 is amplified by an amplifier63 to provide an amplified receiver signal. The source 65 is alsoamplified by an inverting amplifier 64 to provide an inverted andamplified receiver signal. The amplification by the amplifier 63 may beless than 1, equal to 1, or more than 1. The amplification by theamplifier 64 may be less than −1, equal to −1, or more than −1. Forexample, the amplifier 63 may be a voltage follower, and the amplifier64 may be an inverter.

Both of the outputs from the amplifiers 63, 64 are provided to a firstswitch 66 and a second switch 76. The first switch 66 switches betweenthe output of the first amplifier 63 and the output of the secondamplifier 64 in accordance with a switching signal 74. The switchingsignal 74 is synchronized with the ultrasonic energy, e.g., theswitching signal 74 is synchronized with the signal used to drive theultrasonic transducer (e.g., the transmitter 11 of FIG. 2).

The second switch 67 also switches between an amplified receiver signaland an inverted and amplified receiver signal in accordance with asecond switching signal 75 (e.g., a quadrature signal). The secondswitching signal 75 is synchronized with the first switching signal 74,and the second switching signal 75 is synchronized with the drivingsignal and has a phase angle that is about 90 degrees out of phaserelative to the first switching signal 74 (as illustrated by the timingdiagram 73).

The circuit 62 also includes a first filter 68 and a second filter 69,which may be integrators. That is, the first filter 68 may integrate thesignal from the first switch (forming an Out X value) and the secondfilter 69 may integrate the signal from the second filter 60 (forming anOut Y value). The first and second filters 68, 69 may integrate for apredetermined amount of time and may also be reset prior to thebeginning of the predetermined amount of time. The magnitude detectioncomponent 70 may determine the magnitude 71 by using Formula 1, providedabove.

FIG. 7 shows a flow chart diagram of a method 76 for detecting air in afluid line, e.g., using the circuit of FIG. 6, in accordance with anembodiment of the present disclosure. The method 76 includes acts 77-81.Act 80 includes acts 82-88, in certain embodiments. Act 81 includes act89, in certain embodiments.

Act 77 transmits ultrasonic energy through a tube. Act 78 receives theultrasonic energy passed through the tube. Act 79 transduces thereceived ultrasonic energy into a receiver signal. Act 80 activelyrectifies the receiver signal to provide a processed signal. Act 81determines whether the processed signal is less that a predeterminedthreshold.

Act 80 may include acts 82-88. Act 82 amplifies the receiver signal witha positive gain using a first amplifier. Act 83 amplifies the receiversignal with a negative gain using a second amplifier. Act 84 switchesbetween outputs of the first and second amplifiers in accordance with afirst switching signal to generate a first switch output. Act 85integrates the first switch output to provide a first integrated output.Act 86 switches between outputs of the first and second amplifiers inaccordance with a second switching signal to generate a second switchoutput. The second switching signal is about 90 degrees out of phasewith the first switching signal. Act 87 integrates the second switchoutput to provide a second integrated output. Act 88 generates aprocessed signal (e.g., a magnitude) using the first and secondintegrated outputs.

As previously mentioned, act 81 may include act 89. Act 89 determinesthat air exists within the tube if the magnitude is less that apredetermined threshold.

FIGS. 8A-8B show a circuit schematic 90 for detecting air in a fluidline using active rectification in accordance with an embodiment of thepresent disclosure.

The circuit 90 receives a receiver signal via connection 97 from areceiver. A first amplifier 91 amplifies the receiver signal and asecond amplifier 92 inverts and amplifies the receiver signal from theconnection 97. The first and second amplifiers 91, 92 use a referencevoltage 115.

A semiconductor device 93 includes switches 98 and 99, which switchbetween the amplified signal from the first amplifier 91 and theamplified and inverted signal from the second amplifier 92. The firstswitch 98 switches in accordance with a first switching signal 100 andthe second switch 99 switches in accordance with a second switchingsignal 101 (e.g., a quadrature signal).

The circuit 90 also includes a first filter 94 and a second filter 95.The output of the first switch 98 is sent to the first filter 94. Theoutput of the second switch 99 is likewise sent to the second filter 95.The first and second filters 94 and 95 are inverting filters. Theoutputs of the first and second filters 94, 95 may be used to calculatea magnitude and thus determine if air exists within a tube, e.g., thetube 6 of FIG. 2.

A reference generating circuit 114 generates the reference voltage 115that is used as a reference from the first and second amplifiers 91, 92,and the first and second filters 94, 95. The reference voltage 115 maybe subtracted out of the results of the first and second filters 94, 95when determining the magnitude.

The first and second switching signals 100 and 101 may be generated by asignal generating circuit 96. The signal generating circuit 96 includesa reference clock 102, a divider 103 (the divider may formed using adual D-type flip flop), and a dual D-type flip flop 104 to generate thefirst and second switching signals 100, 101, such that the secondswitching signal 101 is 90 degrees out of phase relative to the firstswitching signal 100. The first and second switching signals 100, 101generated by the signal generating circuit 96 are fed into thesemiconductor device 93 that includes switches 98 and 99.

FIGS. 9-12 show several signal vs. time traces to illustrate theoperation of the circuit shown in the circuit schematic of FIG. 8 inaccordance with an embodiment of the present disclosure.

FIG. 9 shows a signal trace 105 that is the signal used to drive atransmitter, such as a piezoelectric element, (e.g., the first switchingsignal 100 may be used to drive a piezoelectric element). FIG. 9 alsoshows a signal trace 106 that is the result of the synchronousrectification with no water in a tube (note that it is centered aroundthe reference voltage). The signal trace 106 may be a result from eitherof the outputs from the switches 98 or 99. Note that the signal trace106 shows little relative ac movement around the reference voltage. Whenair exists within the tube, very little (or none) of the ultrasonicenergy reaches the receiver, therefore, the outputs of the first filter94 and the second filter 95 should be about equal to the referencevoltage (however, some offset errors of the amplifiers may skew theresults by a DC voltage).

FIG. 10 shows signal traces 105, 107 and 108. The signal trace 105 isthe voltage applied to the ultrasonic transducer. Trace 107 shows theamplified signal from the first amplifier 91 and trace 108 shows theinverted and amplified signal from the second amplifier 92. FIG. 10shows the case in which water is completely in the tube (i.e., no air islocated between the transmitter). The alternating waveforms (e.g., thetraces 107 and 108) that result from a relative strong receiver signalis a results of the ultrasonic energy reaching the receiver becausethere is water within the tube. That is, the water helps more of theultrasonic energy reach the receiver (e.g., the receiver 8 of FIG. 2).

FIG. 11 shows signal traces 105, 109, and 110. The signal trace 105 isthe voltage applied to the ultrasonic transducer. The signal trace 109shows the result of the synchronous rectification for the in-phasesignal (e.g., the output of the switch 98 of FIGS. 8A-86). The tracesignal 110 shows the filtered, inverted and amplified result of theoutput of the switch 98, i.e., the output of the filter 94. The tracesignal 110 illustrates a condition in which the filtered results from afilter 94 does not deviate much from the reference voltage; in thiscondition, the phase of the signal from the amplifier is such that notmuch of the signal is output from the filter 94, but may insteadpredominantly show up as output from the second filter 95 (see FIGS.8A-86).

FIG. 12 shows signal traces 105, 111, and 112. The signal trace 105 isthe voltage applied to the ultrasonic transducer. Signal trace 111 showsthe results of the synchronous rectification for the quadrature phase,e.g., the output of the second switch 99. Note that the signal trace 111deviates significantly from the reference voltage. Signal trace 112 isthe filtered/inverted/amplified result from the signal represented bythe signal trace 111. That is, the signal trace 112 shows the output ofthe second filter 95. Note that the signal 112 is significantly belowthe reference voltage because water in the tube carries much of theultrasonic energy to the receiver.

FIGS. 13A-15 illustrate a schematic of a circuit 113 for detecting airin a fluid line using active rectification in accordance with anembodiment of the present disclosure. The circuit 113 receives areceiver signal via a connection 300. The circuit 113 includes a firstamplifier 116 and a second amplifier 117. The first amplifier 116 is aninverting amplifier that amplifies and inverts the receiver signal fromthe connection 300. The second amplifier 117 amplifies the receiversignal from the connection 300. A reference generating circuit 200provides a reference voltage to the first and second amplifiers 116,117. The outputs of the first and second amplifiers 116, 117 are fedinto first and second switching networks 118, 119.

The first switching network 118 switches between the amplified signalfrom the second amplifier 117 and the amplified and inverted signal fromthe first amplifier 116. The first switching network 118 is switched inaccordance with a first switching signal. That is, the first switchingnetwork 118 includes a first switch 302 that is a single-pull,single-throw switch and a second switch 304 that is also a single-pull,single-throw switch. The first and second switches 302, 304 switch inaccordance with the first switching signal such that: (1) when the firstswitch 302 is closed, the second switch 304 is open; and (2) when thefirst switch 302 is opened, the second switch 304 is closed. That is,the first switch 302 may receive the first switching signal such that ahigh value from the first switching signal closes the first switch 302,and the second switch 304 receives an inversion of the first switchingsignal that causes the second switch 304 to close when the inversion ofthe first switching signal is high.

The output of the first switching network 118 is fed into a firstintegrator 120 that can be sampled by a first sample-and-hold circuit122 and/or by a second sample-and-hold circuit 123. The firstsample-and-hold circuit 122 works in conjunction with the firstintegrator 120 to integrate the output of the first switching network118 during a time that includes the time in which the ultrasonic energyis received by the receiver. The second sample-and-hold circuit 122works in conjunction with the first integrator 120 to integrate theoutput of the first switching network 118 during a time in which thereceiver signal receives no ultrasonic energy. The secondsample-and-hold circuit 122 integrates the output of the first switchingnetwork 118 to produce a diagnostic signal in order to determine atleast one error that occurs in various places within the circuit 120,such as offset errors in produced by the first and second amplifiers116, 117. The error may be used to adjust the reference voltage to nullout the offset voltages from op-amps contained within the circuit 113that is part of the path which generates the output from the secondsample-and-hold circuit 123. Additionally, alternatively, or optionally,if the diagnostic signal is above a threshold, the CPLD and/or aprocessor may determine that a fault condition exists and may then alarmor halt operation of the infusion pump, for example.

The second switching network 119 switches between the amplified signalfrom the second amplifier 117 and the amplified and inverted signal fromthe first amplifier 116. The second switching network 118 is switched inaccordance with a second switching signal that is 90 degrees out ofphase (or is about 90 degrees out of phase) with the first switchingsignal.

The output of the second switching network 119 is fed into a secondintegrator 121 that can be sampled by a third sample-and-hold circuit124 and/or a fourth sample-and-hold circuit 125. The thirdsample-and-hold circuit 124 works in conjunction with the secondintegrator 121 to integrate the output of the second switching network119 during a time that includes the time in which the ultrasonic energyis received by the receiver. The fourth sample-and-hold circuit 125works in conjunction with the second integrator 121 to integrate theoutput of the second switching network 119 during a time in which noultrasonic energy is received in order to determine at least one error(to produce a quadrature diagnostic signal). The error may be used toadjust the reference voltage to null out the offset voltages fromop-amps contained within the circuit 113 that is part of the path whichgenerates the output from the fourth sample-and-hold circuit 123.

FIG. 14A shows various power supplies used by the circuit 113. FIG. 14Bshows a CPLD 126 that can generate the first and second switchingsignals and can receive various signals. The CPLD 126 can generate thefirst and second switching signals. The CPLD 126 can also generate aninversion of the first switching signal and an inversion of the secondswitching signal.

Furthermore, the CPLD 126 receives the gross comparison signals from thecomparators 129-136 shown in FIG. 15. A high-threshold circuit 127generates a high threshold reference value, and a low-threshold circuit128 generates a low threshold. The high and low thresholds are used bythe comparators 129-136. The outputs of the comparators 129-136 are fedto the CPLD 126. In some embodiments, the CPLD 126 uses only the outputsof the comparators 129-136. However, in some specific embodiments of thepresent disclosure, the CPLD 126 is coupled to an analog-to-digitalconverter so that the CPLD 126 can receive one or more digital signalsthat represent an analog signal, such as the analog OUTPUT signal (i.e.,the output of the first sample-and-hold circuit 122), the analogOUTPUT_DIAG signal (i.e., the output of the second sample-and-holdcircuit 123), the analog OUTPUT_QUAD_DIAG signal (i.e., the output ofthe third sample-and-hold circuit 124), and the analog OUTPUT_QUADsignal (i.e., the output of the fourth sample-and-hold circuit 124);this allows the CPLD 126 to use these signals without the need for thecomparators 129-136 (however, the comparators 129-132 may still bepresent for redundancy, in some embodiments).

The comparator 129 compares the output of the first integrator 122 tothe high threshold. The comparator 130 compares the output of the firstintegrator 122 to the low threshold. The comparator 131 compares theoutput of the second integrator 122 (e.g., the quadrature output) to thehigh threshold. The comparator 132 compares the output of the secondintegrator 122 to the low threshold.

The comparator 133 compares the output diagnostic to the high threshold.The comparator 134 compares the output diagnostic to the low threshold.The comparator 135 compares the output quadrature diagnostic to the highthreshold. The comparator 136 compares the quadrature output diagnosticto the low threshold.

When one of the comparators 129-132 outputs a true value (after anappropriate sample-and-hold has been performed), then the CPLD 126 maydetermine that water exists within the tube. When none of thecomparators 129-132 are true, the CPLD 126 may determine that air existswithin the tube. Comparators 133-136 may be used to determine that thereis a fault condition which is causing the circuit to malfunction.

FIGS. 16-19 show several signal vs. time traces to illustrate theoperation of the circuit shown in the circuit schematic of FIGS. 13A-15in accordance with an embodiment of the present disclosure.

FIG. 16 shows the synchronous rectification switch control signals 138and 139 (e.g., a first switching signal 138 and an inverse of the firstswitching signal 139 used to control the two switches 302, 304 withinthe switching network 118). FIG. 16 also shows the integrated result 140of the synchronous rectification (e.g., the output of the integrator120). An active portion 141 of the integrated result 140 is shown inwhich the receiver receives the ultrasonic energy.

FIG. 17 shows the results 145 of the integrator (e.g., the output of theintegrator 120) which includes a portion 142 that corresponds to waterand a portion that corresponds to the diagnostic result 143. Thereceiver signal 144 is also shown for reference. Note that in theportion 143 that corresponds to the diagnostic portion, the “ping” hadlargely dissipated. The diagnostic portion 143 may be sampled by asample-and-hold circuit (e.g., the sample-and-hold circuit 123 of FIG.13C) which may be used to adjust the voltage fed into the op-amps as areference such that the reference voltage nulls out some of the op-amperrors). FIG. 18 shows various output voltages for the output of thesample-and-hold circuits 122, 123, 124, 125 for the condition in whichthe tube has no water, and FIG. 19 shows the condition in which the tubedoes have water. The output values of the sample-and-hold circuits 122,123, 124, 125 are summarized in chart 146 of FIG. 17 for variousconditions.

FIG. 18 shows several traces 401-411 to illustrate various signals ofthe circuit 113 of FIGS. 13A-15. FIG. 18 shows the condition in whichair is within the tube. Signal trace 401 is the signal sent to drive thetransmitting ultrasonic transducer. Signal trace 402 is the output ofthe first integrator 118. Signal trace 403 is the output of the secondintegrator 119. Signal trace 404 is the analog signal from the receivervia connection 300. Signal trace 405 is the signal sent to the secondand third sample-and-hold circuits 123, 124 to signal them to sample andhold the diagnostic signals (i.e., to generate the OUTPUT_DIAG and theOUTPUT_QUAD_DIAG signals).

Signal trace 406 is the signal sent to the first and fourthsample-and-hold circuits 122, 125 to signal them to sample and hold theoutputs of the integration results (i.e., to generate the OUTPUT and theOUTPUT_QUAD signals). Signal trace 407 is the integrator reset signal toreset the first and second integrators 120, 121. Signal traces 408 and409 are the switching signals sent to the second switching network 119.Signal trace 410 and 411 are the switching signals sent to the secondswitching network 119.

FIG. 19 shows several traces 501-511 to illustrate various signals ofthe circuit 113 of FIGS. 13A-15. FIG. 19 shows the condition in whichwater is within the tube. Signal trace 501 is the signal sent to drivethe transmitting ultrasonic transducer. Signal trace 502 is the outputof the first integrator 118. Signal trace 503 is the output of thesecond integrator 119. Signal trace 504 is the analog signal from thereceiver via connection 300. Signal trace 505 is the signal sent to thesecond and third sample-and-hold circuits 123, 124 to signal them tosample and hold the diagnostic signals (i.e., to generate theOUTPUT_DIAG and the OUTPUT_QUAD_DIAG signals).

Signal trace 506 is the signal sent to the first and fourthsample-and-hold circuits 122, 125 to signal them to sample and hold theoutputs of the integration results (i.e., to generate the OUTPUT and theOUTPUT_QUAD signals). Signal trace 507 is the integrator reset signal toreset the first and second integrators 120, 121. Signal traces 508 and509 are the switching signals sent to the second switching network 119.Signal trace 510 and 511 are the switching signals sent to the secondswitching network 119.

Referring now to FIGS. 18 and 19, note that when water is present withinthe tube, the outputs 502, 503 of the integrators 118, 119 deviatesignificantly more from the reference voltage than when there is waterwithin the tube as shown in traces 402, 403.

FIG. 20 shows a schematic 147 for providing a compensating referencevoltage in accordance with an embodiment of the present disclosure. Thatis, the circuit 147 receives the diagnostic signal 148 from thesample-and-hold circuit 123 which is fed through a connection 148. Theoutput of the circuit 147 may be used as the compensating referencevoltage for the op-amps and/or elsewhere within the circuit 113 of FIGS.13A-15 (or any other embodiment described herein that uses a referencevoltage). The circuit 147 adjusts the reference voltage 149 to supplythe op-amps with a compensating reference voltage 400 (i.e., thecompensating reference voltage) so that the diagnostic signals approachthe reference voltage 149. That is, the compensating reference voltage400 is adjusted to compensate for voltage errors of the op-amps. Asecond circuit 147 may be used to adjust the op-amps of the quadratureoutput (e.g., such as the opamp of the second integrator 121) by usingthe output quadrature diagnostic (e.g., the output of the thirdsample-and-hold circuit 124 of FIG. 13C).

FIGS. 21A and 21B show the operation of the compensating referencevoltage 400 starting from power on, demonstrating how the integratorreference voltage 400 converges on the correct value to null out offseterrors and provides optimal sensitivity to the signal indicating thepresence of water. Signal trace 601 shows the compensating referencevoltage from an offset adjusting circuit 151 of FIG. 22B (describedbelow) and signal trace 602 shows the compensating reference voltagefrom an offset adjusting circuit 152 of FIG. 22B (described below).

FIGS. 22A-23B show a circuit 150 for detecting the presence of airwithin a tube in accordance with another embodiment of the presentdisclosure. The circuit 150 includes wires 306 to receive a receiversignal from a receiver, a first amplifier 308 (inverting), a secondamplifier 310 (non-inverting), a first switching network 312 thatswitches in accordance with a first switching signal, a second switchingnetwork 314 that switches in accordance with a second switching signal(e.g., a quadrature switching signal), a first integrator 153, a secondintegrator 154, and first, second, third and fourth sample-and-holdcircuits 316, 318, 320, 322. The circuit 150 also includes a CPLD 155.

The portion of the circuit 150 shown in FIG. 22A-22C is similar to thecircuit 113 shown in FIG. 13; however, the circuit 150 includes anoffset adjusting circuit 151 to provide a compensating reference voltageto the first integrator 153, and the circuit 150 also includes anotheroffset adjusting circuit 152 to provide a compensating reference voltageto a second integrator 154. The circuit 151 provides the compensatingreference voltage by feeding the output of the sample-and-hold circuit318 (i.e., the OUTPUT_DIAG signal) thereto. The circuit 152 provides thecompensating reference voltage by feeding the output of thesample-and-hold circuit 3120 (i.e., the OUTPUT_QUAD_DIAG) thereto.

The circuit 150 also includes a CPLD 155 to generate the first andsecond switching signals, control the reset of the first and secondintegrators 153, 154, control the sample-and-hold circuits 316, 318,320, 322, receive the outputs of the sample-and-hold circuits 316, 318,320, 322, and issue an alarm and/or alert based upon any detected air asdescribed herein.

FIGS. 24A-26C show a circuit 156 that can detect air in two tubes. Thatis, the circuit 156 includes circuitry 157 (see FIGS. 25A-25C) to detectair in a first tube using synchronous rectification. The circuit 156also includes circuitry 158 (see FIGS. 26A-26C) to detect air in asecond tube using synchronous rectification. The operation of thecircuit 156 may be controlled by a CPLD 158 shown in FIG. 24B.

Various alternatives and modifications can be devised by those skilledin the art without departing from the disclosure. Accordingly, thepresent disclosure is intended to embrace all such alternatives,modifications and variances. Additionally, while several embodiments ofthe present disclosure have been shown in the drawings and/or discussedherein, it is not intended that the disclosure be limited thereto, as itis intended that the disclosure be as broad in scope as the art willallow and that the specification be read likewise. Therefore, the abovedescription should not be construed as limiting, but merely asexemplifications of particular embodiments. And, those skilled in theart will envision other modifications within the scope and spirit of theclaims appended hereto. Other elements, steps, methods and techniquesthat are insubstantially different from those described above and/or inthe appended claims are also intended to be within the scope of thedisclosure.

The embodiments shown in the drawings are presented only to demonstratecertain examples of the disclosure. And, the drawings described are onlyillustrative and are non-limiting. In the drawings, for illustrativepurposes, the size of some of the elements may be exaggerated and notdrawn to a particular scale. Additionally, elements shown within thedrawings that have the same numbers may be identical elements or may besimilar elements, depending on the context.

Where the term “comprising” is used in the present description andclaims, it does not exclude other elements or steps. Where an indefiniteor a definite article is used when referring to a singular noun, e.g.,“a,” “an,” or “the,” this includes a plural of that noun unlesssomething otherwise is specifically stated or the context clearlyindicates otherwise. Hence, the term “comprising” should not beinterpreted as being restricted to the items listed thereafter; it doesnot exclude other elements or steps, and so the scope of the expression“a device comprising items A and B” should not be limited to devicesconsisting only of components A and B. This expression signifies that,with respect to the present disclosure, the only relevant components ofthe device are A and B.

Furthermore, the terms “first,” “second,” “third,” and the like, whetherused in the description or in the claims, are provided fordistinguishing between similar elements and are not necessarily fordescribing a sequential or chronological order. Likewise, these termsare not for indicating an order of importance or relative criticality ofthe referred-to elements. It is to be understood that the terms so usedare interchangeable under appropriate circumstances (unless clearlydisclosed otherwise) and that the embodiments of the disclosuredescribed herein are capable of operation in other sequences and/orarrangements than are described or illustrated herein.

What is claimed is:
 1. A system for detecting air, the systemcomprising: a transmitter configured to transduce a driver signal toultrasonic vibrations; a receiver configured to receive the ultrasonicvibrations and transduce the ultrasonic vibrations to provide a receiversignal; and an air-detection circuit in operative communication with thereceiver to process the receiver signal to generate a processed signalcorresponding to detected air, the air-detection circuit comprising atleast one active-rectifying element configured to actively rectify thereceiver signal to provide the processed signal.
 2. The system accordingto claim 1, the system further comprising: a first conductive path toprovide a first polarity of the receiver signal from the receiver; asecond conductive path to provide a second polarity of the receiversignal from the receiver; a first switch electrically coupled to thefirst and second conductive paths, the first switch configured to switcha first switch output to between the first and second polarities of thereceiver signal, the first switch defining the at least oneactive-rectifying element; a second switch electrically coupled to thefirst and second conductive paths, the second switch configured toswitch a second switch output to between the first and second polaritiesof the receiver signal; a first amplifier having a positive input and anegative input, wherein the positive input is coupled to the firstswitch output and the negative input is coupled to the second switchoutput, wherein the first amplifier provides a first amplifier output inaccordance with the positive and negative inputs; and a first filterelectrically coupled to the first amplifier output of the firstamplifier to provide a first filter output; a third switch electricallycoupled to the first and second conductive paths, the third switchconfigured to switch a third switch output to between the first andsecond polarities of the receiver signal; a fourth switch electricallycoupled to the first and second conductive paths, the fourth switchconfigured to switch a fourth switch output to between the first andsecond polarities of the receiver signal; a second amplifier having apositive input and a negative input, wherein the positive input of thesecond amplifier is coupled to the third switch output and the negativeinput of the second amplifier is coupled to the fourth switch output,wherein the second amplifier provides a second amplifier output inaccordance with the positive and negative inputs; and a second filtercoupled to the second amplifier to provide a second filter output. 3.The system according to claim 2, wherein the second filter is anotherintegrator.
 4. The system according to claim 2, wherein the secondfilter is a low-pass filter.
 5. The system according to claim 4, whereinthe another integrator is reset after a predetermined period ofintegration time.
 6. The system according to claim 2, wherein at leastone of the third and fourth switches are electronically controlled. 7.The system according to claim 2, wherein: the first and second switchesare configured to receive a first switching signal, the first switchingsignal and the first and second switches are configured to switch apolarity of the electrical coupling between the first amplifier and thereceiver in accordance with the first switching signal, and the thirdand fourth switches are configured to receive a second switching signal,the second switching signal has a phase angle of 90 degrees relative tothe first switching signal, the second switching signal and the thirdand fourth switches are configured to switch a polarity of theelectrical coupling between the second amplifier and the receiver inaccordance with the second switching signal.
 8. The system according toclaim 7, wherein at least one of the first switching signal and thesecond switching signal is a digital signal embodied in a digitalcircuit.
 9. The system according to claim 7, wherein at least one of thefirst switching signal and the second switching signal is an analogsignal.
 10. The system according to claim 7, wherein the processedsignal is a square root of: a squared first filter output summed with asquared second filter output.
 11. The system according to claim 7,wherein a processor determines that air exists in a fluid tube when theprocessed signal is below a predetermined threshold.
 12. The systemaccording to claim 11, wherein the processor estimates a bubble volumeusing the flow rate of fluid within the tube and a period of time theprocessed signal is below the predetermined threshold.
 13. The systemaccording to claim 2 wherein: the first and second switches areconfigured to receive a first switching signal, the first and secondswitches switch in response to the first switching signal, the first andsecond switches switch such that the first switch output is coupled tothe first polarity of the receiver signal about when the second switchoutput is coupled to the second polarity, the first and second switchesswitch such that the first switch output is coupled to the secondpolarity of the receiver signal about when the second switch output iscoupled to the first polarity, the third and fourth switches areconfigured to receive a second switching signal, the third and fourthswitches switch in response to the second switching signal, the thirdand fourth switches switch such that the third switch output is coupledto the first polarity of the receiver signal about when the fourthswitch output is coupled to the second polarity, and the third andfourth switches switch such that the third switch output is coupled tothe second polarity of the receiver signal about when the fourth switchoutput is coupled to the first polarity.
 14. The system according toclaim 13, wherein the first and second switching signals each has afrequency at least substantially the same as a frequency of theultrasonic vibrations.
 15. The system according to claim 13, wherein thefirst and second switching signals each has a frequency at leastsubstantially the same as a frequency of the driver signal.
 16. Thesystem according to claim 13, wherein the first switching signal has aphase angle of about 90 degrees relative to the second switching signal.17. The system according to claim 13, wherein the first switching signalhas a phase angle of 90 degrees relative to the second switching signal.18. The system according to claim 1, the system further comprising: afirst single pole, single throw switch defining the at least oneactive-rectifying element configured to provide electrical communicationbetween the receiver signal and a first switch output in accordance witha first switching signal; and a second single pole, single throw switchconfigured to provide electrical communication between the receiversignal and a second switch output in accordance with an inverted signalof the first switching signal.
 19. The system according to claim 18,wherein at least one of the first switching signal and the invertedsignal of the switching signal is a digital signal embodied in a digitalcircuit.
 20. The system according to claim 18, wherein at least one ofthe first switching signal and the inverted signal of the switchingsignal is an analog signal.
 21. The system according to claim 18, thesystem further comprising a first amplifier configured to amplify thereceiver signal prior to electrical coupling with the first single pole,single throw switch.
 22. The system according to claim 18, the systemfurther comprising a second amplifier configured to amplify the receiversignal prior to electrical coupling with the second single pole, singlethrow switch.
 23. The system according to claim 18, the system furthercomprising: a third single pole, single throw switch configured toprovide electrical communication between an inversion of the receiversignal and a third switch output in accordance with a second switchingsignal; and a fourth single pole, single throw switch configured toprovide electrical communication between the inversion of the receiversignal and a fourth switch output in accordance with an inverted signalof the switching signal.
 24. The system according to claim 23, thesystem further comprising an amplifier configured to amplify theinversion of the receiver signal prior to electrical communication withone of the third and fourth single, pole, single throw switches.
 25. Thesystem according to claim 23, wherein the first and second switchingsignals have a quadrature phase relationship.
 26. The system accordingto claim 23, the system further comprising a first integrator, whereinthe first switch output and a second switch output are in electricalcommunication with the first integrator to integrate a signal therefromto provide a first integrator output.
 27. The system according to claim26, wherein the first integrator is reset after a first predeterminedperiod of time.
 28. The system according to claim 26, further comprisinga first sample-and-hold circuit configured to operatively sample andhold the first integrator output.
 29. The system according to claim 26,the system further comprising a second integrator, wherein the thirdswitch output and the fourth switch output are in electricalcommunication with the second integrator to integrate a signal therefromto provide a second integrator output.
 30. The system according to claim29, wherein the second integrator is reset after a second predeterminedperiod of time.
 31. The system according to claim 29, further comprisinga second sample-and-hold circuit configured to operatively sample andhold the second integrator output.
 32. The system as in one of claim 23,wherein the first and second switching signals are synchronized to thedriver signal.
 33. The system according to claim 1, wherein theprocessed signal is a square root of: a squared first integrator outputsummed with a squared second integrator output.
 34. The system accordingto claim 1, further comprising a processor configured to determinewhether air exists when the processed signal is below a predeterminedthreshold.
 35. The system according to claim 1, wherein the first andsecond integrators integrate for a predetermined number of cycles. 36.The system according to claim 1, wherein the first integrator integratesfor a predetermined number of cycles of the driver signal for apredetermined period of time after the driver signal drives thetransmitter such that the ultrasonic vibrations have passed thereceiver, wherein a first integrator output is used to adjust an offsetof the first integrator.
 37. The system according to claim 36, wherein:the second integrator integrates for the predetermined period to captureall of the ultrasonic vibrations passing the receiver, and a secondintegrator output is used to adjust an offset of the first second. 38.The system according to claim 1, further comprising a first integrator,wherein a first switch output and a second switch output are inelectrical communication with the first integrator to integrate a signaltherefrom to provide a first integrator output. a second integrator,wherein a third switch output and a fourth switch output are inelectrical communication with the second integrator to integrate asignal therefrom to provide a second integrator output. a firstsample-and-hold circuit to hold a voltage of the first integrator outputfor the processor to determine the processed signal; a first diagnosticsample-and-hole circuit to hold the voltage of the first integratoroutput to adjust an offset of the first integrator; a secondsample-and-hold circuit to hold a voltage of the second integratoroutput for the processor to determine the processed signal; and a seconddiagnostic sample-and-hole circuit to hold the voltage of the secondintegrator output to adjust an offset of the second integrator.
 39. Thesystem according to claim 38, wherein the processed signal is a vectordefined by the first integrator output and the second integrator output,wherein a processor is configured to perform an integrity check bydetermining if a phase angle of the processed signal is within apredetermined range.
 40. A method of detecting air, the methodcomprising: transmitting ultrasonic energy; receiving the ultrasonicenergy; transducing the received ultrasonic energy into a receiversignal; actively rectifying the receiver signal to provide a processedsignal; and determining whether the processed signal is less that apredetermined threshold.
 41. The method according to claim 40, whereinthe act of actively rectifying the receiver signal to provide theprocessed signal includes: inverting the receiver signal to provide aninverted receiver signal; switching between the receiver signal and theinverted receiver signal in accordance with a first switching signal toprovide a first switch output; integrating the first switch output toprovide a first integrated output; switching between the receiver signaland the inverted receiver signal in accordance with a second switchingsignal to provide a second switch output; integrating the second switchoutput to provide a second integrated output; and calculating amagnitude using the first and second integrated outputs, wherein themagnitude defines the processed signal.
 42. The method according toclaim 41, wherein the act of actively rectifying the receiver signal toprovide the processed signal includes: activating a first switchingnetwork configured to switch between the receiver signal and an invertedreceiver signal to provide a first switching network signal; switchingbetween the receiver signal and the inverted receiver signal inaccordance with a first switching signal to provide the first switchingnetwork signal; integrating the first switching network signal toprovide a first integrated output; activating a second switching networkconfigured to switch between the receiver signal and an invertedreceiver signal to provide a second switching network signal; switchingbetween the receiver signal and the inverted receiver signal inaccordance with a second switching signal to provide the secondswitching network signal, wherein the second switching signal is about90 degrees out of phase with the first switching signal; integrating thesecond switching network signal to provide a second integrated output;and generate a processed signal using the first and second integratedoutputs.
 43. The method according to claim 42, wherein the firstswitching network comprises two single pole, double throw switches. 44.The method according to claim 42, wherein the second switching networkcomprises two single pole, double throw switches
 45. The methodaccording to claim 42, wherein the processed signal is a magnitudecalculated by using the first and second integrated outputs.
 46. Themethod according to claim 40, wherein the act of actively rectifying thereceiver signal to provide a processed signal comprises: amplifying thereceiver signal with a positive gain using a first amplifier; amplifyingthe receiver signal with a negative gain using a second amplifier;switching between outputs of the first and second amplifiers amplifiesin accordance with a first switching signal to generate a first switchoutput; filtering the first switch output to provide a first filteredoutput; switching between the outputs of the first and second amplifiersto generate a second switch output, wherein the second switching signalis one of equal to or about equal to ninety degrees out of phase withthe first switching signal; filtering the second witching output toprovide a second filtered output; and generating a processed signalusing the first and second filtered outputs.
 47. A circuit comprising: areceiver connection configured to provide a receiver signal; and anair-detection circuit in operative communication with the receiverconnection to process the receiver signal to generate a processed signalcorresponding to detected air, the air-detection circuit comprising atleast one active-rectifying element configured to actively rectify thereceiver signal to provide the processed signal.